Conventionally, a seating area adjuster is known which adjusts a length of a seating surface of a seat cushion so that a user can be seated in a comfortable posture corresponding to his/her size. Such apparatus is placed in the seat cushion and is provided with a roller at a tip portion. By means of a movement of the roller in a back and forth direction, a tip portion of the seat cushion is protruded forward and retracted backward and the length of the seating surface in the back and forth direction can thereby be adjusted.
Generally, the seating surface of the seat cushion is made of leather, fabric, or the like, which is hardly retractable. The cushion member made of resin foam, or the like, is arranged at a backside of a skin member for a buffer effect. In order to avoid a generation of wrinkle because of a looseness of the hardly retractable skin member and to avoid an application of an excessive tensile force relative to the seating member in a condition where the length of the seating surface in the back and forth direction is changed, a spring for applying an appropriate tensile force to the seat skin member is provided.
According to a seating area adjuster disclosed in JP06-284940A, the spring for applying the tensile force to the skin member is engaged with an end of the skin member at a first end and is engaged with a support frame at a second end. Therefore, when the roller moves forward for lengthening the seating surface, the skin member is applied with an increased spring force at the tip end portion of the seat cushion. On this occasion, the cushion member is more compressed than it was before an adjustment of the seating member. Thus, the cushion member becomes harder and the buffer effect of the cushion member may occasionally be reduced. The tip end portion of the seat cushion is in contact with femoral region of the user which is sensitive in comfortable ride. Therefore, an appropriate buffer effect of the seat cushion is required to be maintained for realizing a comfortable sense of use. In order to make up for decrease in the buffer effect of the cushion member, a spring having a low spring constant may be applied for restricting an increase in the tensile force. However, the spring size may be increased and the manufacturing cost and the weight of the adjuster may be increased.
According to a seating area adjuster disclosed in JPU07-013244, an end of the spring is engaged with a lever which is rotated in response to an adjusting operation of the seating surface. Therefore, an increase in spring force can be eased. However, it is difficult to equalize a movement amount of the roller with a movement amount of the lever. Thus, the increase in the spring force may not be prevented in a condition where the length of the seating area is adjusted. Further, the cushion member may be superfluously compressed. With the configuration of the seating area adjuster disclosed in JPU07-013244, the spring is also required as well as the seating area adjuster disclosed in JP06-284940A.
A need thus exists to realize a seating area adjuster having a low-cost structure which maintains an invariable buffer effect of the cushion member at any adjusted position of the seating surface without using the spring for applying the tensile force to the skin member.